CAN FD is a communication protocol that evolved from the CAN protocol developed by BOSCH and which is widely used in automotive and other applications. CAN is described in the ISO 11898 specification. With CAN and also with CAN FD, data is transmitted in data packets referred to as frames. The frame format of CAN FD is however different compared to CAN. Notably, a CAN FD frame may comprise data portions transmitted at different bit rates. More specifically, a CAN FD frame may comprise an arbitration phase in which a normal bit rate is used followed by a data phase in which a high bit rate higher than the normal bit rate is used. In a CAN frame, in contrast, the normal bit rate is used throughout the frame.
A CAN network may comprise devices which support CAN FD as well as devices which do not. For example, a CAN network may comprise a first and a second device supporting both CAN and CAN FD, and a third device supporting only a CAN. In this case, the first and the second device may communicate with each other using CAN FD and with the third device using CAN.
A problem may arise in that a CAN device receiving a CAN FD frame may detect the CAN FD frame as errored, possibly resulting in an unjustified error counter overflow. Furthermore, a non CAN FD passive device used within a selective wakeup (SWU) partial networking (PN) network may initiate an unnecessary wakeup in response to receiving a CAN FD frame, due to detecting the frame as errored. This may cause unnecessary power consumption.
A CAN device suitable for operating in a CAN SWU/PN network may be desired to be CAN FD passive. A CAN FD passive device is a device which, roughly speaking, ignores any received CAN FD frame and takes no action in response to the CAN FD frame. More specifically, a CAN FD passive device should not, in response to receiving a CAN FD frame, perform any of the following actions: (1) initiating a wakeup procedure, (2) interpreting the frame content, (3) indicating that the frame is errored, (4). incrementing or decrementing its internal receiver (RX) error counter (REC). The CAN FD passive device should however be capable of detecting a CAN frame received before or after the CAN FD frame.
A CAN frame may be in the CAN base format or in the CAN extended format. Similarly, a CAN FD frame may be in the CAN FD base format or in the CAN FD extended format. These formats are specified in “CAN with flexible data rate—specification—version 1.0” released by BOSCH on Apr. 17, 2012, which is incorporated herein by reference.